1. Technical Field
Embodiments relate to a substrate assembly comprising capacitive interconnections, and to a manufacturing method thereof.
2. Discussion of the Related Art
It is known to provide electrical connections of an ohmic type between a plurality of chips and/or between chips and a substrate. Said connections envisage the formation of protuberances or bumps, in particular solder bumps or pillar bumps, extending from respective facing portions of the chips and of the substrate. The electrical connections using bumps present numerous advantages as compared to electrical connections using wires (wire bonding), amongst which the possibility of enabling a considerable saving of area.
For example, U.S. Pat. No. 5,477,933 describes an electronic device comprising a chip connected to a substrate using a plurality of bumps.
Each bump, for example made of Au—Ge and/or Pb—Sn, is arranged in direct electrical contact with respective connection regions formed on respective facing surfaces of the chip and of the substrate, and in this way forms a conductive interconnection.
However, with the increase in the factor of integration of electronic devices, in the last few years it has become increasingly difficult to provide a sufficient amount of high-performance interconnections, which are in particular able to transfer both power signals and information signals, above all high-frequency signals (for example, in the case of RFID devices, devices functioning at radiofrequency, etc.). To overcome these difficulties, devices have been proposed the interconnections of which use a coupling of a capacitive and/or inductive type. In this case, the ohmic connections used for transfer of information signals are replaced by capacitive connections, which enable an efficient transfer of AC signals. A capacitive connection can be made by forming conductive pads on the surfaces of the chips that are to be coupled, and then by arranging the chips so that the respective conductive pads face one another to form a capacitor. It is evident that, in order to maximize the performance, the distance between facing conductive pads should be controlled in a precise, reliable, and repeatable way. Furthermore, also the alignment between conductive pads that are to communicate should be controlled.
To solve these problems, document No. US 2005/0046037 describes a first substrate and a second substrate provided with respective conductive pads configured for capacitive coupling. The first substrate moreover includes a recess in which a bump (in particular, a solder bump) is formed. The recess and the bumps are configured so that, when the second substrate is brought up to the first substrate coming into contact with the bump, all the conductive pads are separated from one another by a predetermined distance, in any case less than the thickness of the bump.
With reference to the capacitive interconnections described in document No. US 2005/0046037, the distance between the conductive pads of the facing substrates is determined jointly by the thickness of the bumps and by the depth of the recesses in which the bumps are formed. Possible process spread or non-uniformity of the manufacturing steps can lead to formation, on one the same substrate, of recesses having non-uniform depths and/or bumps having non-uniform thicknesses. Furthermore, to enable a sufficient degree of mechanical stability and support between coupled substrates, it may be necessary to form the bumps in a number much higher than what is effectively necessary for the transfer of information signals between substrates. In particular, in the case where the transfer of information signals were effected exclusively using the capacitive coupling between conductive pads, all the bumps would have the sole function of support and separation between conductive pads.
This results in a considerable waste of area of the substrates used, moreover complicating the manufacturing process thereof and increasing the costs thereof on account of the need to dig the substrate in a plurality of portions for providing the recesses in which the bumps are formed.